Compressor of turbo machine and its compressor wheel

ABSTRACT

The invention provides a compressor of a turbo machine and its compressor wheel that do not easily undergo breaking even when rotated at a high number of revolutions. The compressor of the turbo machine includes a male screw portion integrally formed on a main body portion of the compressor wheel and a male screw portion disposed at a distal end of a shaft for driving the compressor wheel that are coupled with each other through a sleeve equipped at one of the ends thereof with a female screw portion capable of meshing with the male screw portion of the compressor wheel and at the other end with a female screw portion capable of meshing with the male screw portion of the shaft.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a compressor of a turbo machine and its compressor wheel.

2. Description of the Related Art

A compressor of a turbo machine of the type that is rotated by a turbine wheel via a shaft by utilizing energy of an exhaust gas as means for increasing an intake amount of an engine by compressing air and drives a centrifugal type compressor wheel coupled with a shaft is known as a turbo charger.

FIG. 7 is a sectional side view of the turbo charger 11 according to the prior art. The turbo charger 11 includes an exhaust-side unit 12 for taking out energy of revolution from the exhaust gas of an engine and an intake-side unit 13 for compressing air by this energy of revolution and sending compressed air into the engine.

A turbine wheel 14 is imparted with energy and is rotated by the exhaust gas inflowing from an exhaust inflow passage 19. A centrifugal type compressor wheel 16 for compressing air is fitted on the opposite side to the turbine wheel 14 of a shaft 23 (hereinafter called a “distal end side of the shaft 23”) through the shaft 23. A fitting hole 25 penetrates through a center of the compressor wheel 16. The shaft 23 is fitted into the fitting hole 25 with slight loose fit or tight fit. The compressor wheel 16 is fixed to the shaft 23 as a nut 26 is fastened to a male screw portion 40 formed at a distal end of the shaft 23.

FIG. 8 is a sectional side view of the compressor wheel 16 shown in FIG. 7. A main body portion 29 of the compressor wheel 16 includes an inlet-side disk portion 29A and a back surface-side disk portion 29B. A plurality of vane portions 18 are arranged on the outside of the main body portion 29 and the fitting hole 25 penetrates through the center of the main body portion 29.

To accomplish lightweight, the compressor wheel 16 is produced from a casting such as an aluminum alloy. Because rotating speed of the compressor wheel 16 reaches high values of dozens of thousands of rounds per minute (rpm), centrifugal force resulting from the high-speed revolution imparts an extremely high tensile strength in a radial direction and sometimes invites breaking of the compressor wheel 16. It is known that this breaking is likely to particularly develop in the inner wall of the fitting hole 25 as the starting point.

To solve this problem, a technology described in Patent Reference (JP-A-5-504178), for example, is known.

FIG. 9 is a sectional view of a compressor wheel 16 according to this Patent Reference. A fitting hole penetrating through the compressor wheel 16 is not disposed but a fitting hole 42 having a female screw is formed at its lower part. A male screw is formed at a distal end 54 of a shaft 23. A male screw is formed at the distal end 54 of the shaft 23. The shaft 23 and the compressor wheel 16 are coupled with each other as the distal end 54 is screwed into the fitting hole 42.

However, the prior art technology shown in FIG. 8 is not free from the following problem. In other words, it has been confirmed that breaking of the inner wall of the fitting hole 25 in the compressor wheel 16 occurs particularly frequently in the proximity of the maximum outer circumferential portion 30 at which the outer circumferential portion of the compressor wheel 16 becomes maximal in an axial direction.

According to the prior art shown in FIG. 9, the fitting hole 42 is disposed in the proximity of the maximum outer circumferential portion 30 in the axial direction. Therefore, when rotating speed is increased, breaking may occur from near the maximum outer circumferential portion 30.

Particularly when an engine equipped with the turbo charger 11 using the compressor wheel 16 is used for work machines such as construction machines, a high load state such as a loading operation (that is, a high rotating speed of the turbocharger) and a state almost free from the load (that is, a low rotating speed) are repeated within short time intervals. As a result, the stress amplitude applied to the compressor wheel 16 becomes high and breaking is more likely to occur.

A technology called “EGR (Exhaust Gas Recirculation)” has been adopted in recent years as a counter-measure for reducing nitrogen oxides (NOx) contained in an exhaust gas of a Diesel engine. This technology returns a part of the exhaust gas emitted from the engine to an intake system of the engine for re-circulation. To accomplish EGR, it is necessary to secure fresh air for combustion capacity in a cylinder where the quantity of fresh air becomes smaller by the re-circulation amount of the exhaust gas and to achieve a higher-pressure ratio of the turbo charger 11. In other words, the compressor wheel 16 must be rotated at a higher rotating speed. The prior art technology is not yet sufficient and a compressor wheel 16 having higher durability has been desired.

SUMMARY OF THE INVENTION

In view of the problems described above, the invention aims at providing a compressor of a turbo machine exhibiting less breaking even when rotated at a high rotating speed and its compressor wheel.

To accomplish this object, a compressor of a turbo machine according to the invention includes a male screw portion integrally formed on a main body portion of a compressor wheel and a male screw portion disposed at a distal end of a shaft for driving the compressor wheel that are coupled with each other through a sleeve equipped at one of the ends thereof with a female screw portion capable of meshing with the male screw portion of the compressor wheel and at the other end with a female screw portion capable of meshing with the male screw portion of the shaft.

In the invention, a diameter of the male screw portion of the compressor wheel may be greater than a diameter of the male screw portion of the shaft.

In the invention, at least either one of centering between the compressor wheel and the sleeve and centering between the sleeve and the shaft may be made in a spigot joint arrangement.

In the invention, a seal groove may be formed around an outer circumferential portion of the sleeve and a seal ring may be fitted into the seal groove so as to prevent leakage of air and oil between a back surface chamber of the compressor wheel and a bearing chamber.

The invention may also have a construction which includes a thrust bearing fixed to a non-rotary member not executing revolution in synchronism with the shaft and a disk-like thrust collar fixed to the shaft, and wherein the thrust collar and the sleeve sandwich the thrust bearing between them.

In the invention, a distal end of a cylindrical portion of a back surface-side disk portion of the compressor wheel is a male screw processed portion.

The following can be listed up as the effects of the invention.

The fitting hole or aperture for coupling with the shaft need not be disposed in the compressor wheel main body portion. As a result, the stress acting on the compressor wheel becomes small and breaking becomes less even when the compressor wheel is rotated at a high number of revolutions.

The compressor wheel is formed in many cases of a material having a lower intensity than the shaft to reduce the weight. Therefore, when the male screw portion of the compressor wheel is rendered thick, the problem that the male screw portion of the compressor wheel is particularly likely to be broken becomes small and overall durability can be improved.

When the rotation balance of the compressor wheel and the turbine wheel is individually adjusted and these wheels are assembled, a centering error after assembly becomes small. Therefore, the frequency of re-adjustment of the rotation balance of the compressor of the turbo machine becomes small.

Members for sealing air and oil need not be disposed separately, and air and oil can be sealed with a compact construction.

It is also possible to support the thrust bearing with a simple construction and to effectively bear the force in the thrust direction that acts on the shaft.

Because breaking of the compressor wheel becomes more difficult to occur and durability can be improved, the pressure ratio of the turbo charger using this compressor wheel can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a compressor wheel according to the invention;

FIG. 2 is a sectional view of FIG. 1;

FIG. 3 is a sectional view of a turbo charger according to the invention;

FIG. 4 is a detailed view of a portion P in FIG. 3;

FIG. 5 is a flowchart showing a procedure for assembling the compressor wheel;

FIG. 6 is a graph showing the relation between an inner diameter of a known fitting hole and a magnitude of a stress;

FIG. 7 is a sectional side view of a turbo charger according to a prior art;

FIG. 8 is a sectional side view of a compressor wheel shown in FIG. 7; and

FIG. 9 is a sectional view of another compressor wheel according to the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the invention will be hereinafter explained in detail with reference to the accompanying drawings.

Referring to FIG. 3, an exhaust-side unit 12 includes an exhaust-side housing 15 and a turbine wheel 14 having a plurality of vanes and supported by a shaft 23.

The exhaust-side housing 15 has an exhaust inflow passage 19 for supplying an exhaust gas to the turbine wheel 14. The exhaust inflow passage 19 is formed into an annular shape in such a manner as to encompass the outer periphery of the turbine wheel 14 and is connected to an engine exhaust flow passage through which the exhaust gas emitted from an engine, not shown, flows. The exhaust-side housing 15 has also an exhaust outflow port 21 for emitting the exhaust gas after imparting energy to the turbine wheel 14. The exhaust outflow port 21 is formed substantially into a cylindrical shape that is concentric with the center of revolution of the turbine wheel 14. An opening on the opposite side to the exhaust outflow port 21 is closed by an exhaust-side inner plate 22.

The shaft 23 is formed integrally with the turbine wheel 14. The shaft 23 penetrates through the exhaust-side inner plate 22 and is rotatably supported by a bearing 24. The turbine wheel 14 and the shaft 23 are ordinarily formed of a nickel base super-alloy, carbon steel or alloy steel.

A compressor wheel 16 is accommodated inside an intake-side housing 17. The intake-side housing 17 has an intake inflow port 27 for sucking air into the compressor wheel 16. The intake inflow port 27 is formed substantially into a cylindrical shape that is concentric with the center of revolutions of the compressor wheel 16. An opening on the opposite side to the intake inflow port 27 is closed by an intake-side inner plate 55.

Air that is compressed by the compressor wheel 16 is centrifugally discharged and is supplied to a feed port of the engine, not shown, while passing through an intake exhaust passage 28 annularly formed in such a manner as to encompass the outer peripheral portion of the compressor wheel 16.

The vanes 18 include full vanes 18A having a large width in an axial direction of the vanes and intermediate vanes 18B in which a vane inlet starts from an intermediate part in the axial direction with respect to the full vanes 18A. These full vanes 18A and intermediate vanes 18B are alternately arranged.

A group of rotary members including the turbine wheel 14, the compressor wheel 16 and the shaft 23 will be hereinafter called the “rotary members”. A group of stationary members including the intake-side housing 17, the exhaust-side housing 15 and a bearing housing 45 will be hereinafter called the “non-rotary members”. A penetrating direction of the fitting hole 25 will be called the “axial direction”.

As shown in FIGS. 1 and 2, a main body portion 29 of the compressor wheel 16 according to the invention is solid and does not have any fitting holes or apertures.

A portion for sucking air into the compressor wheel 16 will be called a“compressor wheel inlet portion 35” and a portion for discharging air in a radial direction will be called a “compressor wheel outlet portion 33”. A curve surface of an intermediate portion between the compressor wheel inlet portion 35 and the compressor wheel outlet portion 33 will be called a “disk center portion 34”.

A portion in the axial direction at which the outer peripheral portion of the compressor wheel 16 becomes maximal will be called the “maximum outer peripheral portion 30”. The main body portion 29 of the compressor wheel 16 has an inlet-side disk portion 29A and a rear surface-side disk portion 29B. A cylindrical portion 43 is integrally arranged on the rearmost portion of the rear surface-side disk portion 29B while its axis is in alignment with the main body portion 29. A male screw 44 having a smaller diameter than that of the cylindrical portion 43 is integrally formed at the lower end of the cylindrical portion 43. The male screw 44 will be called a “compressor wheel male screw portion 44”.

Processing for securing a width across flats or nut-like processing, for example, is applied to the outer peripheral portion of the compressor wheel inlet portion 35 of the compressor wheel 16 and this portion can be clamped by use of a wrench, or the like.

Referring to FIGS. 3 and 4, the distal end portion 60 of the shaft 23 fixed to the turbine wheel 14 is precisely machined into a cylindrical shape that is concentric with the shaft 23. This cylindrical portion will be called a “shaft cylindrical portion 60”. A male screw 46 is formed at a further distal end of the shaft cylindrical portion 60. This male screw 46 will be called a “shaft male screw portion 46”. The outer diameter of the shaft male screw portion 46 is smaller than the outer diameter of the compressor wheel male screw portion 44. The shaft male screw portion 46 and the compressor wheel screw portion 44 are connected to each other through a sleeve 49 having female screws at both of its ends.

As shown in FIG. 4, spigot joint processing is applied to the inner peripheral portion 58 at the end of the sleeve 49 on the side of the shaft 23 with respect to the shaft cylindrical portion 60. A female screw 53 (hereinafter called a “shaft-side female screw portion 53”) meshing with the shaft male screw portion 46 is formed at the depth of the inner peripheral portion 58 (on the side of the compressor wheel 16).

Spigot joint processing is applied to the inner peripheral portion 57 at the end of the sleeve 49 on the side of the compressor wheel 16 with respect to the cylindrical portion 43 formed on the rear surface of the compressor wheel 16. A female screw 52 (hereinafter called a “compressor wheel-side female screw portion 52”) meshing with the compressor wheel male screw portion 44 is formed at the depth of the inner peripheral portion 57 (on the side of the shaft 23).

Incidentally, the shaft-side female screw portion 53 and the compressor wheel-side female screw portion 52 in the sleeve 49 are shown penetrated but they need not always be penetrated. Processing for securing a width across flats or nut-like processing, for example, is applied to the outer peripheral portion 61 of the of the sleeve 49 on the side of the compressor wheel 16 and this portion can be clamped by use of a wrench, or the like. A seal groove 50 is formed in the entire outer peripheral portion at an intermediate part of the sleeve 49 in the axial direction and a seal ring 51 formed of an FC material, etc, is fitted into the seal groove 50. The seal ring 51 is formed in such a manner that when force for reducing the diameter is applied, the outer peripheral portion of the sealing ring 51 tightly fits into the inner peripheral portion of the intake-side inner plate 55.

The bearing 24 is accommodated in a bearing box 63 of the bearing housing 45 that connects the intake-side housing 17 and the exhaust-side housing 15. An oil-feed port 59 is formed in the bearing housing 45 to supply a lubricant to the bearing 24 and the thrust bearing 48.

FIG. 5 is a flowchart showing the procedure for assembling the compressor wheel 16 into the shaft 23. First, a disk-like thrust collar 47 having a round hole at its center is fitted to the shaft 23 supported by the bearing 24 (Step S11).

Next, the thrust bearing 48 is fitted to the bearing housing 45 (Step S12). An oil passage 56 through which lubricant oil flows is disposed in the thrust bearing 48.

The sleeve 49 is screwed into the shaft 23 (Step S13). In this instance, the sleeve 49 is screwed into the shaft male screw portion 46 while the outer peripheral portion 61 of the sleeve 49 processed into the nut shape is clamped by the wrench, or the like. In consequence, the sleeve 49 and the thrust collar 47 rotate integrally with the shaft 23.

Next, the intake side inner plate 55 is fixed to the bearing housing 45 (Step S14). Consequently, the thrust bearing 48 is fixed to the non-rotary members while being sandwiched between the bearing housing 45 and the intake-side inner plate 55.

As a result, the thrust bearing 48 fixed to the non-rotary members in Step S13 is sandwiched between the thrust collar 47 and the sleeve 49 as the rotary members rotating integrally with the shaft 23. Therefore, the force imparted in the thrust direction of the shaft 23 during revolution is received by the thrust bearing 48 and the position in the axial direction is limited. When the sleeve 49 is screwed in Step S14, the outer peripheral portion of the seal ring 51 comes into adhesion with the inner peripheral portion of the intake-side inner plate 55. Consequently, the oil for lubricating the bearing 24 and the thrust bearing 48 is prevented from flowing out to the space (called a “back surface chamber 62”) of the back surface of the compressor wheel 16.

Next, the compressor wheel 16 is screwed into the sleeve 49 (Step S15). In this instance, the nut-like processed portion of the compressor wheel inlet portion 35 of the compressor wheel 16 and the nut-like processed portion of the outlet portion of the turbine wheel 14 are screwed to each other while being clamped by the wrench, or the like. The compressor wheel 16 and the shaft 23 are thus coupled with each other.

As explained above, in the invention, the compressor wheel male screw portion 44 is arranged round the outer periphery of the cylindrical portion 43 at the rearmost surface portion of the back surface-side disk portion 29B of the compressor wheel 16. The impeller male screw portion 44 and the shaft male screw portion 46 disposed at the distal end of the shaft 23 are connected to each other through the sleeve 49 having the female screw portions 52 and 53 at both of its ends.

Therefore, even when the compressor wheel 16 is solid, the compressor wheel 16 and the shaft 23 can be connected to each other. For this reason, the stress acting on the compressor wheel 16 becomes small and breakage does not occur even at a high rotating speed.

FIG. 6 is a graph showing the relation between the inner diameter Φ of the fitting hole 25 of the compressor wheel 16 and the magnitude of the stress T acting on the compressor wheel 16 at the maximum outer circumference portion 30 at which the outer circumferential portion of the compressor wheel 16 becomes maximal in the axial direction of the rotary shaft of the compressor wheel 16 in the prior art technology. In the graph, the stress T is small when the inner diameter of the fitting hole 25 is 0 and becomes extremely great when the inner diameter is excessively small. At a certain inner diameter D or above, the stress T becomes greater with the increase of the inner diameter of the fitting hole 25. Therefore, it can be understood that when the fitting hole 25 does not exist and the compressor wheel 16 is solid as in the present invention, the stress becomes small.

According to the invention, the diameter of the compressor wheel male screw portion 44 formed integrally with the compressor wheel 16 is greater than the diameter of the shaft male screw portion 46 formed at the distal end of the shaft 23. The compressor wheel 16 and the compressor wheel male screw portion 44 are formed of a casting of an aluminum alloy, for example. On the other hand, the shaft 23 and the shaft male screw portion 46 are formed of a hard material such as iron or its alloy. Therefore, when the thickness of the casting of the aluminum alloy having a lower strength is increased, it is possible to prevent the problem that one of them is particularly likely to be broken.

Furthermore, the shaft male screw portion 46 is formed at the distal end portion of the shaft 23 and the sleeve 49 having the female screw portion 53 is screwed to the shaft male screw portion 46. This configuration makes it possible to reduce the outer diameter of the portion of the shaft 23, which is supported by the shaft 24, when compared to the configuration in which, for example, a female screw is disposed in the shaft 23. Therefore, because the speed of the outer peripheral portion of the shaft 23 becomes lower, the rotation frictional loss with the bearing 24 becomes smaller and breaking of the shaft 23 and the bearing 24 does not easily occur.

The seal groove 50 is disposed around the outer circumferential portion of the sleeve 49 and the oil can be sealed by a compact construction. Because the sleeve 49 and the compressor wheel 16 are centered with each other in the spigot joint, unbalance during revolution can be reduced.

Incidentally, the outer circumferential portion of the compressor wheel inlet portion 35 of the compressor wheel 16 is sufficient so long as the compressor wheel 16 can be fixed when screwed to the sleeve 49 and may have a bolt shape having a hexagonal boss, for example.

The invention has been explained about only its application example to the turbo charger but can be similarly applied to other turbo machines and mechanical driving centrifugal compressors such as a micro-gas turbine. 

1. A compressor of a turbo machine comprising: a compressor wheel male screw portion integrally disposed on a main body portion of a compressor wheel; a shaft male screw portion disposed at a distal end of a driving shaft of the compressor wheel; and a sleeve equipped at one of the ends thereof with a compressor wheel-side female screw portion capable of meshing with the compressor wheel male screw and at the other end thereof with a shaft-side female screw portion capable of meshing with the shaft male screw portion; the compressor wheel screw portion and the shaft male screw portion being coupled with each other through the sleeve.
 2. The compressor of a turbo machine as defined in claim 1, wherein a diameter of the compressor wheel male screw portion is greater than a diameter of the shaft male screw portion.
 3. The compressor of a turbo machine as defined in claim 1, wherein at least one of centering between the compressor wheel and the sleeve and centering between the sleeve and the shaft is made by means of a spigot joint arrangement.
 4. The compressor of a turbo machine as defined in claim 2, wherein at least one of centering between the compressor wheel and the sleeve and centering between the sleeve and the shaft is made by means of a spigot joint arrangement.
 5. The compressor of a turbo machine as defined in claim 1, which further comprises a seal groove formed around an outer circumferential portion of the sleeve and a seal ring fitted into the seal groove so as to prevent leakage of air and oil between a back surface chamber of the compressor wheel and a bearing chamber.
 6. The compressor of a turbo machine as defined in claim 2, which further comprises a seal groove formed around an outer circumferential portion of the sleeve and a seal ring fitted into the seal groove so as to prevent leakage of air and oil between a back surface chamber of the compressor wheel and a bearing chamber.
 7. The compressor of a turbo machine as defined in claim 3, which further comprises a seal groove formed around an outer circumferential portion of the sleeve and a seal ring fitted into the seal groove so as to prevent leakage of air and oil between a back surface chamber of the compressor wheel and a bearing chamber.
 8. The compressor of a turbo machine as defined in claim 4, which further comprises a seal groove formed around an outer circumferential portion of the sleeve and a seal ring fitted into the seal groove so as to prevent leakage of air and oil between a back surface chamber of the compressor wheel and a bearing chamber.
 9. The compressor of a turbo machine as defined in claim 5, which further comprises a thrust bearing fixed to a non-rotary member not executing revolution in synchronism with the shaft and a disk-like thrust collar fixed to the shaft, and wherein the thrust collar and the sleeve sandwich the thrust bearing between them.
 10. The compressor of a turbo machine as defined in claim 6, which further comprises a thrust bearing fixed to a non-rotary member not executing revolution in synchronism with the shaft and a disk-like thrust collar fixed to the shaft, and wherein the thrust collar and the sleeve sandwich the thrust bearing between them.
 11. The compressor of a turbo machine as defined in claim 7, which further comprises a thrust bearing fixed to a non-rotary member not executing revolution in synchronism with the shaft and a disk-like thrust collar fixed to the shaft, and wherein the thrust collar and the sleeve sandwich the thrust bearing between them.
 12. The compressor of a turbo machine as defined in claim 8, which further comprises a thrust bearing fixed to a non-rotary member not executing revolution in synchronism with the shaft and a disk-like thrust collar fixed to the shaft, and wherein the thrust collar and the sleeve sandwich the thrust bearing between them.
 13. A compressor wheel of a compressor of a turbo machine, wherein a distal end of a cylindrical portion of a back surface-side disk portion of a compressor wheel is a male screw processed portion. 